1. Field of the Invention
The present invention relates to remote controlled, unmanned inspection vehicles. More specifically, the present invention relates to inspection vehicles capable of entry into highly constrained spaces, and traversing nonhorizontal and/or nonflat ferromagnetic surfaces through magnetic adhesion to such surfaces.
2. Description of the Related Art
It is frequently necessary to perform inspections of machinery, storage tanks, etc, where highly constrained entry points and/or environmental hazards make direct human inspection either impossible or inadvisable. Examples include electrical generators and other machinery having highly constrained travel spaces between the various moving components, storage tanks wherein chemical hazards are present, such as underground gasoline tanks, and pools containing nuclear reactor spent fuel wherein radiation hazards are present. Frequently, access to various regions that must be inspected requires traversing nonhorizontal surfaces, such as angled components and/or walls, and/or nonflat surfaces, such as the exterior or interior of pipes.
One proposed remote controlled inspection vehicle is described in U.S. Pat. No. 5,363,935, issued to H. Schempf et al. on Nov. 15, 1994. The vehicle includes at least one frame member supporting a continuous track, a magnet, a fixed magnetic element, and a movable magnetic element. The movable magnetic element forms one side of a rotatable cylinder surrounding the drive shaft operatively connecting the motor and tracks, so that it may engage the drive shaft when movement is desired. The fixed magnetic element includes a pair of magnetic pieces on either side of the cylinder, with one piece including the permanent magnet, and legs terminating in rollers contacting the tracks. Each track cleat includes a nonmagnetic center portion and magnetic end portions. When the movable magnetic  element is in a first position wherein it forms a magnetic flux path between the fixed magnetic pieces, thereby forming a complete flux path including the movable piece, 2 fixed pieces, ends of the track cleats, and the surface upon which the vehicle is travelling, the vehicle is magnetically secured to the inside surface of the tank. When the movable magnetic element is rotated to its second position, the magnetic flux path is broken, and the vehicle is not magnetically secured to the interior surface of the tank. A pair of such frame units are connected to either end of a sensor unit through steering units. An alternative embodiment utilizes a track wherein the cleats are made from magnetic material with copper bars extending across the width of each end of the cleats, and a ferromagnetic plate extending across the length of the plate. The ferromagnetic plate is surrounded by a coil in electrical contact with the copper bars at each end. Electrical current is supplied to additional copper bars adjacent to the track, so that when the copper bars extending across the width of the track are brought into contact with these copper bars, the cleat becomes an electromagnet. The steering unit includes a yaw actuator and a pitch actuator, both of which are actuated by electric motors and gear arrangements. Sensors may include ultrasonic inspection sensors, cameras, acoustic navigation systems, vapor sensors, radiation detectors, etc. A tether line is used to supply power and control functions. This patent does not describe a means for rotating the tracks of the vehicle around their longitudinal axis.
U.S. Pat. No. 4,828,059, issued to S. Naito et al. on May 9, 1989, describes a wall-crawling machine having permanent magnets within the tracks. One embodiment uses two sets of tracks, pivotally connected with each other, so that movement of the rear track towards a wall causes the forward track to align itself with the wall and adhere to the wall. Movement of the front track up the wall then angles the rear track to align it with the wall. A second embodiment utilizes permanent magnets attached to a pivoting arm to pull the vehicle up onto a wall. A third embodiment has laterally-extendable tracks for performing a transverse walking function.
U.S. Pat. No. 4,664,212, issued to K. Nagatsuka et al. on May 12, 1987, describes a remote controlled, tracked vehicle having suction chambers with apertures in the tracks. A centrally mounted suction apparatus is mounted adjacent to the  central portion of each track, and sucks air through the suction chambers located near the central portion of the vehicle to retain the vehicle on a surface.
U.S. Pat. No. 5,894,901, issued to N. Awamura et al. on Apr. 20, 1999, describes an endless magnetic track for a vehicle, having a plurality of magnets coupled in series with the chain, and a means for providing slack within the tracks when traversing uneven terrain.
Accordingly, a remote controlled inspection vehicle capable of fitting into extremely small spaces, for example, between the rotor and stator of an electrical generator, is desired. Additionally, a remote controlled inspection vehicle having propulsion units that are rotatable about their longitudinal axis for traversing concave and convex surfaces, for example, the interior and exterior of pipes, is desired. Further, a remote controlled inspection vehicle having an adjustable distance between the propulsion tracks is desired. A remote controlled inspection vehicle having replaceable modular tracks for different operations is also desired.